254 
FXUS66 KPDT 161056
AFDPDT

Area Forecast Discussion
National Weather Service Pendleton OR
256 AM PST Mon Dec 16 2019

.SHORT TERM...Today through Thursday...Freezing fog/low stratus 
is widespread through the upper Columbia Basin of WA. Southerly 
winds in central OR and through the Blue Mountain foothills are 
preventing fog from encroaching south. These winds may ease or 
shift slightly allowing fog to develop through the Blue Mountain 
foothills and Columbia Basin of OR before morning. In the
meantime, longwave ridge axis will set up over the area today 
while longwave trough off the western US coast deepens. Ridge axis
will assist in maintaining sharp surface temp inversion. Due to 
this and generally light winds, fog and stratus will be slow to 
mix today, if at all. Currently expecting some brief clearing late
in the day before another night of widespread freezing fog. Dense
fog advisories may be needed if mixing fails to occur at all or 
if fog layer deepens tonight. 

Ridge shifts east Tuesday night and begins to open the region up 
to deep S/SSW flow aloft. Encroaching trough will tighten a
southerly pressure gradient that is expected to elevate winds in
Central OR and the Blue Mountains Tuesday and Tue night. As 
usual, there is particular concern for gusty conditions in the 
Grande Ronde Valley where winds are expected to be 35-40mph. 
Though moisture and cloud cover will begin overspreading the area
Tuesday into Tue night, much of the initial precip will remain 
along the Cascade crest and westward given the flows orientation 
along the mountains. As precip chances increase, snow levels
support snow for the Cascade and Blues and rain for the majority
of the Columbia Basin. Initial precipitation may be mixed for the
Kittitas and Yakima valleys as narrow tongue of warm air advects 
over the area in advance of the landfalling low. clark 

.LONG TERM...Thursday through Monday...Rather active and wet
period is likely for the end of the week into the weekend. Surge 
of moisture will arrive early Thursday bringing good chances for 
lower elevation rain and mountain snow. Snow levels Thursday 
morning will range from ~1200 feet in the Washington Cascades as 
well as Blue/Wallowa Mountains to near 3500 feet in the Oregon 
Cascades where a few inches of snow is expected. By Thursday 
afternoon, warmer air will rapidly move into the Oregon Cascades 
and Columbia Basin of Oregon & Washington with snow levels 
increasing to 5500-6000 feet. The exception will be across the 
Washington Cascades where minor cold air damming will keep snow 
levels between 2500-3500 feet. With a continued stream of moisture
over the Washington Cascades, winter weather headlines may be 
needed for the latter half of the week. 

While snow levels will gradually increase, subfreezing overnight low 
temperatures are likely across the Yakima/Kittitas Valleys as well 
as portions of the lower Columbia Basin in Washington and will allow 
for slight chances of freezing rain both Thursday and Friday 
morning. A warm front gradually lifts north through the area Friday 
night into Saturday morning bringing slowly diminishing 
precipitation chances through the weekend. The most likely areas to 
see continued precipitation chances through the day Monday will be 
along the Cascade crests as well as higher terrain of central and 
northeast Oregon. Richards


&&

.AVIATION...


&&

.PRELIMINARY POINT TEMPS/POPS...
PDT  41  25  37  23 /   0   0   0   0 
ALW  40  28  35  25 /   0   0   0   0 
PSC  36  25  34  24 /   0   0   0   0 
YKM  32  22  34  23 /   0   0   0   0 
HRI  37  23  35  24 /   0   0   0   0 
ELN  32  22  32  22 /   0   0   0   0 
RDM  39  21  40  23 /   0   0   0   0 
LGD  36  24  35  23 /   0   0   0   0 
GCD  39  23  37  23 /   0   0   0   0 
DLS  37  25  37  27 /   0   0   0   0 

&&

.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&

$$

91/75/76